Commonly in a printing device, such as a printer and a printing machine, which prints on continuous paper previously provided with fold lines at given intervals as viewed in a paper-feeding direction, a folding device is used to refold the printed continuous paper. In this specification, each of the given intervals is called a top-and-bottom length.
Especially in case that the printing device is an electrophotographic printer, the paper is often heated and pressed in a fixing process. The heating and the pressing make the continuous paper expand and contract. As a result, occasionally, the paper is wrinkled or tensed, and the rigidity of the paper is increased by moisture loss of the paper. Therefore, the folding of the continuous paper is sometimes difficult, so that the above-mentioned folding device is used in many cases.
In general, the folding device is made up of a feeding member for feeding continuous paper, a swinger fin that swings using its one end as a fulcrum like a pendulum in synchronization with fold lines while feeding the continuous paper into its inside, a paddle member for pressing a fold line portion of the continuous paper fed to the swinger fin, a table to be surmounted by the continuous paper that has been folded, a jam-detection sensor for monitoring the continuous paper in the process of being folded on the table and detecting a folding jam, etc. A folding jam here means a state in which the continuous paper is folded or bent in areas other than the preformed fold lines or a state in which there generates a folding defect in a part of a fold line, which is so called tenting.
The paddle member is formed of a pair of paddle units, and in many cases, the distance between the paddle units can be so changed as to correspond to the top-and-bottom length of the continuous paper.
Various data necessary for the folding operation, which includes, for example, the top-and-bottom length, printing speed and the like, is exchanged between the folding device and a printing device, such as a printer and a printing machine, by using proper communication means.
The feed rate of the continuous paper in the folding device is usually set faster than the feed rate of the continuous paper in the printing device. Accordingly, as illustrated in FIG. 5, slack is made in the continuous paper between the printing device and the folding device to monitor the size of the slack using one buffer sensor. Ordinarily, if the slack grows larger, the folding operation of the folding device is carried out. When the slack becomes smaller, the folding operation is suspended. The continuous paper is folded by carrying out the folding operation intermittently while the printing is continuously performed by the printing device.
In recent years, along with the diversification of continuous paper, there is a tendency to print on continuous paper that is thinner than ever before and special-purpose papers called label paper, tack paper, etc.
The thin continuous paper expands and contracts to a large degree due to heating and pressing in the fixing process, and is then liable to be wrinkled and tensed. For this reason, there occurs a folding jam more easily. The thin paper here is thinner than paper that weighs about 64 g/m2 in basis weight.
If the printer or printing device performs the fixing process by a flash-fixing method, a folding jam occurs more often for the following reason. According to the flash-fixing method, a toner-applied area of the printed continuous paper absorbs more energy of flash lights than a non-applied area does. Accordingly, the toner-applied area and the non-applied area are different in heating degree, so that there occur imbalanced expansion and contraction, wrinkles and tension.
In a conventional folding device, when a folding jam occurs, the continuous paper or paper fragments that have caused the jam remain in the inside of the swinger fin. In order to remove them from the inside of the swinger fin, it is required to stick a hand or fingers into the narrow swinger fin. Particularly when the printing is applied onto continuous papers, such as label papers, tack papers and the like, with back sides applied with an adhesive agent and attached onto the peelable paper, if there occurs a folding jam, released labels or the like are stuck to the inside of the swinger fin. It is sometimes extremely difficult to get rid of them.
In the course of long-period use, paper powder, dust, dirt and the like are sometimes firmly stuck in the swinger fin. In order to remove and clean them, the swinger fin has needed to be disassembled.
Generally, in a pair of feed rollers for feeding a sheet-like article such as continuous paper, only one of the feed rollers is driven by a proper driving source (so-called driving roller). In this case, the other feed roller (called a driven roller) is biased by a proper biasing member such as a spring member toward the driving roller, and is pressed against the driving roller through the continuous paper or the like to rotate together.
The conventional folding device has a structure in which only one of a pair of feed rollers located in the swinger fin is driven. As stated above, however, the swinger fin makes a swinging motion using its end portion as a fulcrum. In other words, the swinger fin constantly receives acceleration and deceleration in the swinging direction. Due to the inertia created by the acceleration/deceleration, the driven roller moves away from the driving roller, and a pressing force upon the driving roller is reduced to destabilize the rotation of the driven roller. As a result, the feed of the continuous paper becomes unstable, which occasionally causes a folding jam.
Furthermore, the conventional folding device has a structure in which the pair of feed rollers is provided only to the tip end portion of the swinger fin. With this structure, however, sometimes the continuous paper cannot be stably fed within the swinger fin at a correct rate.
According to the conventional folding device, while the continuous paper is fed in the folding device, the paper gets static electricity due to friction or the like in some cases. Due to attraction of static electricity, friction resistance between the continuous paper and the inner surface of the swinger fin and the like is increased, which hampers the paper feedability. This occasionally causes a folding jam in the swinger fin or on the table to be surmounted by the continuous paper that has been folded.
It is generally ideal for a member that makes a swinging motion using its one end as a fulcrum like a swinger fin 2 to be caused to make a swinging motion of a natural rigid pendulum, or to have a sine wave-like velocity curve. However, in order to mechanically achieve the sine wave-like velocity curve, a cam and a link mechanism are required. To add to such a complicated mechanism, if swing velocity and swing width are changed according to the top-and-bottom length of the paper and the paper feed rate, a more complicated adjustment mechanism is furthermore required.
If a pulse motor is employed as a driving source of the swinger fin, it is possible to relatively easily obtain a pseudo-sine wave-like curve by properly controlling the frequency of drive pulses and the number of applied pulses. Even in this case, however, in order to change the swing velocity and the swing width so as to corresponding to the top-and-bottom length of the paper and the feed rate, it is required to maintain the frequency and the number of the applied pulses in the form of a table as many as there are combinations of top-and-bottom lengths and feed rates.
In some cases, the sine wave-like velocity curve is given up, and simple trapezoidal velocity control is carried out. In this case, a gradient of velocity in the trapezoidal velocity control at the time of acceleration/deceleration is fixed. Therefore, when the top-and-bottom length of the paper is changed, swinging time at the maximum swing velocity is also changed. This causes the disadvantage that the swinging motion of the swinger fin becomes unnatural, and that smooth paper folding is discouraged.
In the electrophotographic printer, the paper is often heated and pressed in the fixing process as described, and the heating and the pressing sometimes contracts the continuous paper. Due to the contraction, the continuous paper comes off the feeding member of the folding device, and travels obliquely or meanderingly in the folding device instead of traveling through a proper feed path. The oblique travel and the meandering travel often cause a folding jam. As illustrated in FIG. 7, however, jam detection sensors 104a and 104b of the conventional folding device monitor the continuous paper in the process of being folded on the table. Therefore, if the oblique or meandering travel occurs, the sensors often fail to immediately detect them. The folding operation and the feed of the continuous paper are not stopped until a folding jam is detected, so that there have been the problem that a large quantity of folding-jammed continuous paper is produced.
Thin continuous paper has a great degree of paper expansion/contraction caused by the heating and the pressing in the fixing process. This produces the problem that the oblique or meandering travel is liable to occur, incurring more folding-jammed continuous paper.
In case that the printer or printing device has the fixing process performed by the flash-fusing method, there also is the problem that, due to the imbalanced expansion and contraction of the paper, the oblique or meandering travel more easily occurs, incurring more folding-jammed continuous paper.
In the conventional folding device, the fold lines of the continuous paper in the process of being fed to the swinger fin and folded on the table are pressed by a vane member of the paddle member, whereby the continuous paper is laid on the table. Distance between a pair of paddle units constructing the paddle member of the folding device is often set so as to correspond to the top-and-bottom length of the continuous paper to be folded.
The conventional folding device, however, has sometimes caused a folding defect attributable to a setting mistake or setting failure in respect of the distance between the paddle units, or the like. For example, the distance between the paddle units is mistakenly set to 254 mm (10 inches), 152.4 mm (6 inches) or the like when the top-and-bottom length of the continuous paper to be folded is 203.2 mm (8 inches).
In the conventional art, the vane member rotates at constant rate all the time regardless of travel timing of the fold lines. Accordingly, sometimes not only the fold lines of the continuous paper but also areas other than the fold lines are also pressed by the vane member, and sometimes the vane member hampers the feed of the fold line portions. The vane member has occasionally caused a paper jam or folding defect.
In the conventional folding device, the setting of the continuous paper prior to the folding has been carried out manually by the operator. In order to start a smooth folding operation, the tip end of the continuous paper is preferably set to a preset optimum position, or so-called standby position. However, if the tip end of the continuous paper is set to a wrong position, it is impossible to start a smooth folding operation, which incurs a folding defect from time to time. It is preferable that not only the continuous paper but also the swinger fin, the paddle member, and the table be set to standby positions. In some cases, however, the swinger fin, the paddle member, and the table cause a folding defect by being set to different positions from their respective standby positions.
In the conventional folding device, the direction of the first fold line of the continuous paper to be folded is limited to prescribed one direction, such as a mountain fold. Therefore, if the direction of the first fold direction of the continuous paper is opposite to the prescribed direction, it is required to carry out arrangements including alignment of the folding direction of the first fold line with the prescribed direction by cutting away and discard the first page of the continuous paper.
In many cases, after all the continuous paper is folded, the continuous paper that has been folded on the table is checked. During this process, in the conventional folding device, the swinger fin is in the way for checking the folding condition of the continuous paper. Furthermore, the folded continuous paper is taken out usually after the table is lowered. If the number of laid sheets of the paper is small, the paper is often taken out from the top portion of the table without taking the trouble to lower the table. In this process, the swinger fin gets in the way and hampers the removal of the continuous paper.
According to the conventional folding device, if the continuous paper has sprocket holes in both side edges thereof, the paper sometimes comes off the feeding member of the folding device due to contraction of the continuous paper which is caused by the heating and the pressing in the fixing process of the printing device. For this reason, there occasionally generates a feeding defect of the continuous paper and a folding defect attributable to the feeding defect.
In general, a pair of pin tractors is used as a feeding member of the folding device. Distance between the pin tractors is so fixed as to correspond to the width of the continuous paper, and the pins of the pin tractors are interfitted in the sprocket holes formed in both side-edge portions of the continuous paper, to thereby feed the continuous paper. However, if the continuous paper contracts in the width direction, distance between the sprocket holes of the side-edge portions of the continuous paper becomes shorter than the distance between the pins of the pin tractors due to the contraction. As a result, the pins come off the sprocket holes to produce a feeding defect. Particularly, thin continuous paper contracts to a great degree and causes a feeding defect more often.
In case that the printing device has the fixing process performed by a flash-fusing device, sometimes more feeding defects attributable to contraction of the continuous paper are produced. According to the flash-fixing method, a toner-applied area of the continuous paper absorbs more energy of flash lights than a non-applied area does. Therefore, the toner-applied area and the non-applied area are different in degree of the heating of the continuous paper, so that there often generate fluctuations in contraction degree of the width direction as viewed in the longitudinal direction of the continuous paper.
The conventional folding device performs the folding operation through an intermittent operation as described above. In many cases, a folding defect has been caused at the start of a folding operation during the intermittent operation. The folding defect at the start of the folding operation has occurred more often in case that the continuous paper is thin or that the printing device has the fixing process performed by the flash-fusing method.